Conventionally, there is a so-called separated-type air conditioning apparatus comprising a refrigerant circuit configured by connecting an outdoor unit having a compressor and an outdoor heat exchanger, and an indoor unit having an expansion valve and an indoor heat exchanger.
In this type of air conditioning apparatus, the performance of the indoor unit is regulated according to the indoor temperature setting and other conditions during a refrigeration cycle such as cooling or dehumidifying in which the outdoor heat exchanger is made to function as a refrigerant condenser, and the indoor heat exchanger is made to function as a refrigerant evaporator. The performance of the indoor unit is regulated mainly by controlling the flow rate of refrigerant flowing through the indoor heat exchanger which functions as a refrigerant evaporator, and a method for controlling the aperture of the expansion valve (hereinafter referred to as superheat degree control) so that the degree of superheat of the refrigerant remains constant at the outlet from the indoor heat exchanger functioning as a refrigerant evaporator is sometimes used as the method for controlling the flow rate of refrigerant flowing through the indoor heat exchanger.
In a separated-type air conditioning apparatus, the indoor unit and the outdoor unit are mounted at positions of different height. The mounting conditions of the indoor unit and outdoor unit are such that when the refrigeration cycle is performed in which the indoor heat exchanger is made to function as a refrigerant evaporator, the pressure of the refrigerant supplied to the indoor unit (hereinafter referred to as indoor unit supply pressure) becomes greater or less than the pressure of the refrigerant in the outdoor heat exchanger (hereinafter referred to as condensation pressure) functioning as a refrigerant condenser in accordance with the height difference between the mounting positions of the outdoor unit and indoor unit. Therefore, in cases in which, e.g., the indoor unit is mounted higher than the outdoor unit and the indoor unit supply pressure is less than the condensation pressure, the performance of the indoor unit is insufficient; i.e., the amount of refrigerant flowing through the indoor heat exchanger functioning as a refrigerant evaporator is insufficient. In cases in which the indoor unit is mounted lower than the outdoor unit and the indoor unit supply pressure is greater than the condensation pressure, instead of the performance of the indoor unit being insufficient, the indoor unit supply pressure sometimes increases undesirably and the COP decreases.
To overcome these problems, there is a method for a separated-type air conditioning apparatus whereby refrigerant can be supplied to the indoor unit at the optimal indoor unit supply pressure by setting a target value for the condensation pressure in accordance with the height difference between the mounting positions of the outdoor unit and the indoor unit, as shown in Japanese Laid-open Patent Application No. 2002-349974.